1. Field of the Invention
The present invention relates to a method for cleaning a glass substrate, to a method for fabricating a glass substrate, and to a magnetic disk using a glass substrate so cleaned and fabricated. More particularly, the present invention relates to a method for cleaning a glass substrate and a method for fabricating a glass substrate in which the glass substrate is cleaned by scrubbing, and to a magnetic disk using a glass substrate so cleaned and fabricated.
2. Description of Related Art
Conventionally, as substrates for magnetic disks, there have generally been used aluminum substrates in stationary devices such as desktop computers and servers, and glass substrates in portable devices such as notebook computers and mobile computers. One disadvantage with aluminum substrates is that they are easy to deform and are not hard enough, offering not quite satisfactory smoothness on the substrate surface after polishing. Another disadvantage is that, if a magnetic head happens to touch a magnetic disk, the magnetic film (magnetic recording layer) on an aluminum substrate is prone to exfoliate from the substrate. Under this background, it is expected that glass substrates, less prone do deformation, offering better surface smoothness, and affording higher mechanical strength, will be increasingly used not only in portable but also in stationary devices and in other home information appliances.
The recording capacity of a magnetic disk can be increased by reducing the distance between the surface thereof and a magnetic head. Inconveniently, however, with a reduced distance between a magnetic head and the surface of a magnetic disk, if there is an abnormal projection formed on or foreign matter adhered to the surface of a glass substrate, the magnetic head collides with the projection or foreign matter. Thus, to make it possible to increase the recording capacity of a magnetic disk by reducing the distance from the surface thereof to a magnetic head, it is necessary to eliminate formation of projections on and adhesion of foreign matter to the surface of a glass substrate altogether. For this purpose, it is conventional practice to polish the surface of a glass substrate with abrasive such as cerium oxide to make it smooth enough.
Disadvantageously, however, polishing a glass substrate with abrasive may leave the abrasive firmly adhered to the surface thereof, and even when the glass substrate surface is thereafter cleaned by scrubbing, it is difficult to remove the abrasive firmly adhered thereto. Moreover, forming a magnetic recording layer on the glass substrate surface with the abrasive firmly adhered thereto is likely to produce pin holes in the layer, destabilize the floating characteristics of the head, and otherwise significantly degrade the magnetic recording characteristics.
As a solution, for example, JP-A-2002-074653 proposes performing, after a polishing step, three types of cleaning, namely ultrasonic cleaning using a detergent, cleaning by scrubbing, and ultrasonic cleaning using pure water. As another solution, JP-A-2003-228824 proposes cleaning a glass substrate by a combination of cleaning by scrubbing and cleaning using a water solution of carbon dioxide.
Supposedly, these conventionally proposed technologies help to a certain degree to remove the abrasive or other foreign matter adhered to a glass substrate. Disadvantageously, however, the former technology, requiring three types of cleaning, complicates the cleaning step and lowers productivity; likewise, the latter technology, requiring the introduction of equipment for maintaining and managing the solubility of the gas, complicates the cleaning step and lowers productivity.